1. Field of the Invention
This invention relates to an ink jet printer in which ink droplets appearing at intervals in place of the information recording ink droplets are electrified for a purpose other than information recording.
2. Description of the Prior Art
An ink jet printer is disclosed in, for example, the specification of the U.S. Pat. No. 3,596,275 granted to Richard G. Sweet on July 27, 1971. In the printer of this type, the moment the ink column jetted out of the nozzle is split into droplets, the information recording signal voltage is applied to the charging electrode coupled electrostatically to the ink column. Consequently, the ink droplets are charged according to the information recording signal voltage. The charged ink droplets are deflected when they pass between the deflecting electrodes and then the deflected ink droplets adhere to the recording medium to form an ink dot pattern in the desired positions of the medium.
In order to cause the deflected ink droplet to adhere to a desired position of the recording medium, it is necessary to check the deflection sensitivity of a droplet and to control the amount of charge to be given to the droplets and the magnitude of electric field for deflection in response to the result of the checking. In order to charge the ink droplets properly in response to the information recording signal voltage, the tip portion of the ink column must be exactly charged in accordance with the signal voltage the moment the tip portion separates from the column. The proper electrification of the tip portion of the ink column in accordance with the information recording signal voltage needs the synchronism between the phase of creating ink droplets and that of generating the signal voltage. For this purpose, phase control devices have been invented by Robert I. Keur (U.S. Pat. No. 3,681,778) and Takahiro Yamada, U.S. Pat. No. 3,999,188, filed Dec. 2, 1974, entitled "Ink-Jet Recording Apparatus". Namely, in such an ink-jet recording apparatus, ink droplets are sometimes charged by signals for being used for a purpose excepting information recording, and such droplets are sometimes located between the droplets charged by signals for information recording.
It is well known that when a series of ink droplets are charged in accordance with an information recording signal voltage each ink droplet is electrically affected by the just preceeding one and therefore a system has been proposed which compensates the information recording signal voltage for every ink droplet in accordance with the like signal voltage for the just preceeding ink droplet (U.S. Pat. No. 3,631,511 granted to Robert I. Keur et al). In this case, however, a complicated circuit network is needed since the compensation is effected through the measurement of the information recording signal voltage.